I don't think this has been mentioned (but if it has, please forgive me!) but my sims will autonomously take care of their babies. They'll feed them, play with them if their social bar is down, and change dirty diapers. However, they won't teach toddlers to walk, talk, or use the potty without being told. In the family I'm playing currently, neither parent has the family oriented trait, and they're still constantly playing with their son and taking care of him - it's so sweet!